Many of the bolded characters in the characterization above are apomorphies of subsets of streptophytes along the lineage leading to the embryophytes, not apomorphies of crown-group embryophytes per se.

All groups below are crown groups, nearly all are extant. Characters mentioned are those of the immediate common ancestor of the group, [] contains explanatory material, () features common in clade, exact status unclear.

Age. Davies et al. (2011: 95% credibility intervals) suggested an age for this clade of (259-)219(-174) m.y.; Magallón et al. (2013) suggested that it was about 312 m.y.o., while (259-)219(-174) m.y. is the age suggested by Clarke et al. (2011); the age of a [Gnetales + Pinales] clade is estimated at 181-140.1 m.y. (Naumann et al. 2013).

Ephedra and Welwitschia had diverged by 110 m.y. ago or more, the welwitschioid seedling, Cratonia, from Brazil, being of this vintage (Rydin et al. 2003), while pollen and seeds attributed to a welwitschioid plant are known from the Lower Cretaceous both in Portugal and eastern North America (Friis et al. 2014). Crane (1996) summarized the fossil history of Gnetales (see Won & Renner 2006; Rydin & Friis 2010 for additional references). For a probable Gnetalean fossil from the Permian, some 250-270 m.y.a., see Wang (2004). Both Ephedra and Welwitschia have polyplicate pollen that has a fossil record of ³250 m.y., being common from the Late Triassic onwards. Dilcher et al. (2005) noted that Gnetalean-like (striate/ribbed) pollen was common in both N. and S. Hemispheres; in the former, records are from the Upper Triassic onwards, in the latter, especially in the early Cretaceous from the northern half of South America. The pollen found by Wang (2004) associated with his fossil, Palaeognetaleana auspicia, is of this general kind. However, that fossil was radiospermic and had two complete integuments, a possible third integument being represented by scales, and the arrangement of parts in the cone was spiral, so what it represents is unclear.

Note: Possible apomorphies are in bold. However, the actual level at which many of these features, particularly the more cryptic ones, should be assigned
is unclear. This is partly because many characters show considerable homoplasy, in addition, basic information for all too many is very incomplete, frequently coming from taxa well embedded in the clade of interest and so making the position of any putative apomorphy uncertain. Then there is the not-so-trivial issue of how ancestral states are reconstructed (see above).

Evolution.Divergence & Distribution. Gnetales s.l., i.e., stem-group Gnetales and including the fossil groups above, show considerably more variation than perhaps might have been expected given the small size of the clade. In the Cretaceous in particular the diversity of Gnetales and the possibly related Bennettitales and Erdtmanithecale (all have an elongated micropyle, etc. - see Friis et al. 2011: chapter 5 and the Cycadales page), and several genera of Gnetalean affinity have been described from the Brazilian Crato formation, some 115-112 m.y.o. (Löwe et al. 2013 and references). Polyplicate (ephedroid) pollen was notably common 125-85 m.y.a. in middle latitudes (northern Gondwana), angiosperms and Gnetales perhaps growing togther then (Crane & Lidgard 1980; see also Friis et al. 2014).

Pollination Biology & Seed Dispersal. Ovules of all three extant genera are visited by diptera and other pollinators (see Kato & Inoue 1994 and Labandeira 2005 for references; Bolinder et al. 2015); sweetish droplets exude from the micropyle. For details of the time from pollination to fertilization, short for a gymnosperm, see Williams (2008 and references).

Genes & Genomes. The nuclear genome is small, C values being 1.4-3.5 picograms (Leitch et al. 2001, 2005). All three genera also have very small chloroplast genomes, Welwitschia rather less so than the others, and it has been suggested that this is because they grow in resource-poor environments, but genome size in Pinus, for example, may not be much bigger (see also C.-S. Wu et al. 2007, 2009 and references: other seed plants growing in similar environments?). Up to 18 genes have been lost from the chloroplast (McCoy et al. 2008; C.-S. Wu et al. 2009; Jansen & Ruhlman 2012 and references). Variation in the nad1 intron 2 needs clarification; it is absent in Welwitschia, present in Gnetum, and what is going on in Ephedra is not entirely clear (Gugerli et al. 2001).

Morphology, Anatomy, etc. Although vessels in Gnetum, for example, are commonly described as being derived from circular pits, this has been questioned (e.g. Rodin 1969; Muhammad & Sattler 1982). Although Rodin (1969) suggested that Gnetales lack pits with a margo-torus construction, but they are clearly shown for Ephedra, but not Gnetum, by Eicke (1957). For gelatinous fibres (g-fibres), see Montes et al. (2012); in Ephedra, at least, their presence had nothing to do with bending and they are not associated with wood tissues, so they are not reaction wood (c.f. angiosperms; c.f. Tomlinson et al. 2014). There are nodal girdles of tissue very like transfusion tissue, at least in Ephedra (Beck et al. 1982). For the numbers of veins entering the leaves, see Rydin and Friis (2010). Boyce and Knoll (2002), Nardmann and Werr (2013), and others discuss leaf development; the scale leaves of Ephedra are reductions/

Interpretations of the parts of both the microsporangium- and megasporangium-bearing structures differ substantially (e.g. Gifford & Foster 1989; Hufford 1997a; Mundry & Stützel 2004). In microsporangiate plants of all three extant genera both stamens and non-functional ovules (although pollination droplets may still be produced) are closely associated, although this perhaps least marked in Ephedra (see also Flores-Rentería et al. 2011), and the microsporangiate cones can be interpreted as being compound (Mundry & Stützel 2004), rather like the megasporangiate cones of Pinales. The plants themselves are functionally dioecious. Gnetum ula is reported as having two sperm cells (Singh 1978). Plastid transmission appears to be maternal, at least in Ephedra distachya (Moussel 1978). The megaspore membrane is thin, but is definitely present (Doyle 2006).

For the morphology of Gnetales in the context of that of fossil gymnosperms, see e.g. Doyle and Donoghue (1986a, b) and especially Doyle (2006, 2008b, and references), for mycorrhizae, see Jacobson et al. (1993), and for pollen, see Osborn (2000: comparison with gymnospermous "anthophytes"), Yao et al. (2004: pollen of Gnetales compared with that of Nymphaea colorata), Rydin and Friis (2005: pollen germination) and Tekleva and Krassilov (2009: pollen morphology, inc. fossils). Martens (1971) provides an extensive treatment of the whole group (see also Gifford & Foster 1989), Friedman (1992), Carmichael and Friedman (1996) and Friedman and Carmichael (1997, and references) discuss double fertilization and Friedman (2015) that and much more, Carlquist (1997, 2012b) describes wood anatomy, Takaso (1985 and references) integument morphology, Endress (1997) details of megasporangiate structures, and Hufford (1997a) microsporangium arrangement.

Gnetales - on a long branch - were found to be sister to Cupressaceae, the Gnecup hypothesis, in an analysis of an amino acid matrix derived from chloroplast genomes (Zhong et al. 2010; see also Ruhfel et al. 2014); both quickly-evolving proteins and also proteins in which there appeared to be much parallel evolution in Cryptomeria and the branch leading to all Gnetales were removed. If they were not removed, a clade [Cryptomeria + Gnetales] was obtained (Zhong et al. 2010; see also Moore et al. 2011; C.-S. Wu et al. 2013). Similarly, an analysis of variation in 83 plastid genes strongly suggested a grouping [Pinaceae [Gnetales + other Pinales]], although other relationships could not be entirely rejected (Chumley et al. 2008; see also Ruhfel et al. 2014). Finally, Raubeson et al. (2006) found that Welwitschia grouped with Podocarpus, but this may be due to rate heterogeneity.

Xi et al. (2013b), using much nuclear and plastid data, although they included only ten gymnosperms, found a poorly to moderately supported [Gnetum + Pinaceae] clade in analyses of nuclear genes only. In analyses of chloroplast data a relationship with Cupressaceae was preferred (see also Davis et al. 2014a for the influence of different genomes); in both cases the alternative topology was rejected with a p-value of 0.001. This suggested to Xi et al. (2013b) that the two genomes of Gnetum had different histories. See also X.-Q. Wang and Ran (2014) for discussion; they noted that analyses of different classes of genes resulted in different topologies,.

Thus despite a number of unresolved issues, a position somewhere around Pinales seems most likely for Gnetales. There are some specific points of genomic similarity between Gnetum, etc., and some or all Pinales. Some Pinaceae have lost a number of the chloroplast genes that are missing in Gnetales (Wu et al. 2009). All eleven NADH dehydrogenase genes in the chloroplast of Pinus thunbergii are absent - or are present, but as pseudogenes (Wakasugi et al. 1994); other work suggests that these genes are absent in all Gnetales and Pinales alone (Braukmann et al. 2009, also 2010; Martín & Sabater 2010; Wicke et al. 2011). The rps16 gene in Gnetales and Pinaceae is commonly lost (Wu et al. 2007, 2009). All Pinales sampled have but a single copy of the chloroplast inverted repeat (Strauss et al. 1988; Tsudzuki et al. 1992); nearly all other seed plants have two copies (Raubeson & Jansen 1992; Lackey & Raubeson 2008), and this may be marked by micromorphological changes in the genome. Interestingly, one end of the inverted repeat of Welwitschia has expanded (Welwitschia is derived within Gnetales) with duplication of trnI-CAU and partial duplication of pscbA gene region at the end of the Large Single Copy region, and these match those of the remnant inverted repeat known from Pinus and other Pinaceae, but not other members of Pinales (Margheim et al. 2006; McCoy et al. 2006, 2008: details of relationship depend on methods of analysis; see also Braukmann et al. 2009; Hirao et al. 2009).

There are also some morphological similarities between Pinales and Gnetales, and within the former, perhaps particularly with Pinaceae. The binucleate sperm cells, basic proembryo structure, development of polyembryony, etc., of Ephedra agree with Pinales in general and perhaps Pinaceae in particular. Some Pinus species have mesogenous stomata in which the subsidiary cells are produced from the same initial that gives rise to the guard cells (Gifford & Foster 1989; see also Mundry & Stützel 2004), as in Gnetales. Strobili with both micro- and megasporangia are common as abnormalities in Pinales (Chamberlain 1935; Rudall et al. 2011a) and occur normally in Gnetum. However, wherever Gnetales are placed, they will have numerous apomorphies. Thus although nearly all Pinales have megasporangiate strobili with spirally-arranged ovuliferous scales or modifications of them, Gnetales have decussating bracts (Magallón & Sanderson 2002); loss of the ovuliferous scale, etc., might also be apomorphies (Finet et al. 2010).

Fossils apparently assignable to Ephedraceae are known from the lower Cretaceous in China (Zhou et al. 2003). Rothwell and Stockey (2009) report a fossil from the Lower Cretaceous that has purportedly ancestral characters for Ephedra - two ovules together, and absence of a tubular micropyle and of a structure surrounding the ovule (seed envelope above), but this is unlikely to be assignable to crown group Gnetales. The distinctive pollen of Ephedra has been found inside fossil seeds that are morphologically also Ephedra in late Aptian to Early Albian (early Cretaceous) deposits from Portugal, suggesting that diversification in the genus occurred some 127-110 m.y.a. (Rydin et al. 2004). Indeed, Early Cretaceous fossils of Ephedra have a "modern" morphology, E. paleorhytidosperma having distinctive seeds very like those of the extant E. rhytidosperma (Yang et al. 2005).

Ephedraceae are rather small, shrubby, much-branched, xeromorphic plants that may be readily recognised by their green, photosynthetic stems, often reduced opposite leaves and small cones borne along the shoots.

Evolution.Divergence & Distribution.Ephedra went into severe decline at the end of the Cretaceous, and extant taxa show little genetic divergence and most relationships have little support (Rydin et al. 2010). It moved from the Old to the New World in the Oligocene (41.5-)29.6(-8.8) m.y.a. and to South America in the Miocene (Ickert-Bond et al. 2009). A shift from entomophily to anemophily may perhaps be connected with Caenozoic duversification in the clade (Bolinder et al. 2012). There has been parallel evolution in micromorphological details of the seed envelope (Ickert-Bond & Rydin 2011).

Pollination Biology & Seed Dispersal. Pollination in extant species is usually by wind, but Ephedra foemina is pollinated by insects and i.a. has pollen with a faster settling velocity than that of wind-pollinated taxa, while fossil "ephedroid" pollen also has characteristics of insect pollination with a thick tectum and dense infratectal layer (Bolinder et al. 2015; c.f. Hall & Walter 2011 in part). Because the pollen exine of Ephedra is shed on germination, the male gametophyte is naked. Fertilization occurs 10-15 hours after pollination.

As the seeds ripen, the "outer integument" surrounding the ovule may become fleshy and brightly coloured, or it may dry and become a wing, or it may be faintly nondescript, the seeds then being dispersed by scatter-hoarding rodents (Hollander & Vander Wall 2009).

Genes & Genomes. There has been a great increase in the rate of synonymous substitutions in the mitochondrial genome and chloroplast and nuclear sequences are also divergent compared with those of other seed plants (Mower et al. 2007 and references). The nuclear genome is very variable in size, and can be huge (Ickert-Bond et al. 2014b).

Chemistry, Morphology, etc. Species of Ephedra are pharmacologically very active and contain a number of distinctive secondary metabolites (Caveney et al. 2001). Biswas and Johri (1997) mention the "deep origin of the periderm", a position that should be confirmed. For leaf and nodal anatomy of species of Ephedra with well developed leaves, i.e. long and linear, see Dörken (2014) and Deshpande and Keswani (1963).

For some general information, see Rydin et al. (2004) and the Gymnosperm Database, and for nodal anatomy, see Marsden and Steeves (1955) and Singh and Maheshwari (1962).

Phylogeny. There is little strong phylogenetic structure along the backbone of a 7 plastid gene-2 compartment analysis of extant species of Ephedra, indeed, there is notably little molecular divergence within the genus (Rydin & Korall 2009; Rydin et al. 2010: see also above). The insect-pollinated Ephedra foeminea (see above) may be sister to the rest of the genus.

Clasification. For a classification of Ephedraceae, including fossil members, see Yang (2014).

Age. Ickert-Bond et al. (2010: 95% highest posterior density) suggest ages of (127-)111.3(-87.2) m.y. for divergence within this clade, Won and Renner (2006) ages of (175-)138(-112) m.y., and Magallón et al. (2013) an age of around 81.9 m.y.; on the other hand, the age in Magallón et al. (2015: note topology) was around 239 m.y. ago. See below for fossils placed in Welwitschiaceae.

Siphonospermum, a fossil from the Lower Cretaceous from Northeast China, may be assignable to this part of the tree (Rydin & Friis 2010).

Chemistry, Morphology, etc. For cyclopropenoid acids, similar to those in Malvales, see Aitzetmüller and Vosmann (1998). Rodin (1968) suggested that the reticulate venation of Gnetum, at least, was a modified dichotomizing system.

Bacterial/Fungal Associations. Brundrett (2008, seen viii.2012) summarizes information on the mycorrhizal status of members of Gnetales as a whole.

Genes & Genomes. Horizontal gene transfer of the mitochondrial nad1 intron 2 from flowering plants (an asterid) to an Asian clade of Gnetum seems to have occurred within the last 5 m.y. (Won & Renner 2003).

Chemistry, Morphology, etc. Not surprisingly, the wood of the lianoid taxa is distinctive, with serial cambia being formed. The reaction wood in Gnetum consists of gelatinous extra-xylary (reaction) fibres in the adaxial position (Tomlinson 2001b, 2003; see also Höster & Liese 1966); it is not typical tension wood. See Martens (1971) for the vascularization of the leaves; pairs of vascular bundles leave the central stele in close proximity.

There is vascular tissue in the two outer coverings of the ovule, but vascular bundles barely enter the base of the inner integument. The outer covering in definitely bilobed early in development, the lobes alternating with bracts, but the middle covering is only weakly bilobed (Takaso & Bouman 1986). Although some gametophyte development occurs after fertilization, the ovule increases appreciably in size between pollination and fertilization (Leslie & Boyce 2012).

For reproductive morphology and development, see Sanwal (1962), for mycorrhizae, see Onguene and Kuyper (2001), and for general information, see the Gymnosperm Database.

Welwitschiaceae can immediately be recognised by the two, long leaves that ensheath the stem; these become curled and are dead and torn at the apices. The plant has no trunk as such, but the stem becomes quite massive.

Evolution.Divergence & Distribution.Cratonia cotyledon is a fossil seedling with distinctive cotyledon vasculature very like that of the leaves of Welwitschia, the secondary veins leaving from the primary veins fuse to form an inverted "Y" (Rydin et al. 2003). Cratonia was found in N.E. Brazil and is late Aptian or early Albian in age, perhaps 114-112 m.y. old; other fossils of welwitschiaceous or more generally gnetalean affinity have been found in the same area (Dilcher et al. 2005; Löwe et al. 2013).

Ecology & Physiology.Welwitschia mirabilis grows in the Namib desert close to the ocean; although there is little rain, fogs are frequent - but not where Welwitschia grows (von Willert 1985). Plants may be some hundreds of years old, the two persistent leaves growing at the base and fraying at the apex.

Genes & Genomes. The chloroplast genome of Welwitschia mirabilis is the smallest plastid genome of all non-parasitic land plants that still have inverted repeats (McCoy et al. 2008).

Chemistry, Morphology, etc. Because of the abundant, branched sclereids in the plant, "One might as well try to cut sections of a thick Scotch plaid blanket as to try and cut a stem of Welwitschia without imbedding." (Chamberlain 1935: pp. 388-389).

Kaplan (1997, vol. 1:6) described the seedling as having a haustorial collet (collar). Serial axillary buds are added throughout the course of the long life of the plant, the youngest buds being in the centre of the axil - a branch-like organization? See Martens (1971) for the vascularisation of the bracts of the megasporangia and the complex organisation of the axis of the megasporangiate strobilus.

For female gametophyte development and fertilization, see Friedman (2014, esp. 2015: remarkable), for general information, see the Gymnosperm Database.